U.S. patent application number 12/758741 was filed with the patent office on 2011-10-13 for interference avoidance in white space communication systems.
Invention is credited to Christian Bergljung, Andres Reial, Anders Rosenqvist.
Application Number | 20110250857 12/758741 |
Document ID | / |
Family ID | 43975227 |
Filed Date | 2011-10-13 |
United States Patent
Application |
20110250857 |
Kind Code |
A1 |
Reial; Andres ; et
al. |
October 13, 2011 |
Interference Avoidance in White Space Communication Systems
Abstract
Mobile communication system equipment avoids interfering with
another transmitter's operation. Sensing information indicating
whether the other transmitter's signal has been detected is
received from remote sensors, wherein each of the remote sensors is
situated at a respective one of two or more sensor locations. The
sensing information and information about the sensor locations is
used to ascertain one or more exclusion boundaries needed to avoid
interfering with the other transmitter's use of the spectral
resource. Beamforming parameters are ascertained that will enable
the main node to transmit within one or more predefined
geographical areas except for any portion of a predefined area
located on a far side of the one or more exclusion boundaries. Two
or more adjusted signals are produced as a function of the
beamforming parameters and one or more signals to be transmitted.
The adjusted signals are transmitted from respective ones of two or
more antennas.
Inventors: |
Reial; Andres; (Malmo,
SE) ; Bergljung; Christian; (Lund, SE) ;
Rosenqvist; Anders; (Lund, SE) |
Family ID: |
43975227 |
Appl. No.: |
12/758741 |
Filed: |
April 12, 2010 |
Current U.S.
Class: |
455/114.2 |
Current CPC
Class: |
H04W 64/00 20130101;
H04W 16/14 20130101 |
Class at
Publication: |
455/114.2 |
International
Class: |
H04B 1/04 20060101
H04B001/04 |
Claims
1. A method of operating mobile communication system equipment to
avoid interfering with another transmitter's use of a spectral
resource, wherein the mobile communication system equipment
includes a main node that serves a plurality of user equipments,
the method comprising: operating the main node to receive, from
each one of two or more remote sensors, sensing information that
indicates whether a signal from said another transmitter has been
detected, wherein each of the remote sensors is situated at a
respective one of two or more sensor locations; using the sensing
information and information about the sensor locations to ascertain
one or more exclusion boundaries needed to avoid interfering with
said another transmitter's use of the spectral resource;
ascertaining beamforming parameters that will enable the main node
to transmit within one or more predefined geographical areas except
for any portion of a predefined area located on a far side of the
one or more exclusion boundaries; producing two or more adjusted
signals as a function of the beamforming parameters and one or more
signals to be transmitted; and transmitting the two or more
adjusted signals from respective ones of two or more antennas.
2. The method of claim 1, comprising: generating correlation
results by correlating information about detected transmissions of
said another transmitter with information about contemporaneous
transmissions of the mobile communication system; and using the
correlation results to detect one or more erroneous indications
that the signal from said another transmitter was detected.
3. The method of claim 1, wherein the sensing information indicates
whether the signal from said another transmitter has been detected
in one frequency band.
4. The method of claim 1, wherein the sensing information indicates
whether the signal from said another transmitter has been detected
in any of a plurality of frequency bands.
5. The method of claim 4, comprising: ascertaining beamforming
parameters on a per-frequency-band basis, wherein for each
frequency band, corresponding beamforming parameters enable the
main node to transmit within one or more predefined geographical
areas except for any portion of a predefined area located on a far
side of one or more exclusion boundaries associated with the
frequency band.
6. The method of claim 1, comprising: modifying beamforming
parameters over time in correspondence with modifications in
transmission activity of said another transmitter.
7. The method of claim 1, comprising: receiving, from each one of
two or more remote sensors, sensing information that indicates
whether a signal transmitted by a transmitter associated with the
main node was received at or above a predefined threshold power
level in any portion of the predefined area located on the far side
of the one or more exclusion boundaries.
8. The method of claim 7, comprising: adjusting the beamforming
parameters if the sensing information does indicate that the signal
transmitted by the transmitter associated with the main node was
received at or above the predefined threshold power level in any
portion of the predefined area located on the far side of the one
or more exclusion boundaries.
9. The method of claim 8, comprising: performing the method
iteratively until the sensing information does not indicate that
the signal transmitted by the transmitter associated with the main
node was received at or above the predefined threshold power level
in any portion of the predefined area located on the far side of
the one or more exclusion boundaries.
10. An apparatus for operating mobile communication system
equipment to avoid interfering with another transmitter's use of a
spectral resource, wherein the mobile communication system
equipment includes a main node that serves a plurality of user
equipments, the apparatus comprising: circuitry configured to
operate the main node to receive, from each one of two or more
remote sensors, sensing information that indicates whether a signal
from said another transmitter has been detected, wherein each of
the remote sensors is situated at a respective one of two or more
sensor locations; circuitry configured to use the sensing
information and information about the sensor locations to ascertain
one or more exclusion boundaries needed to avoid interfering with
said another transmitter's use of the spectral resource; circuitry
configured to ascertain beamforming parameters that will enable the
main node to transmit within one or more predefined geographical
areas except for any portion of a predefined area located on a far
side of the one or more exclusion boundaries; circuitry configured
to produce two or more adjusted signals as a function of the
beamforming parameters and one or more signals to be transmitted;
and circuitry configured to transmit the two or more adjusted
signals from respective ones of two or more antennas.
11. The apparatus of claim 10, comprising: circuitry configured to
generate correlation results by correlating information about
detected transmissions of said another transmitter with information
about contemporaneous transmissions of the mobile communication
system; and circuitry configured to use the correlation results to
detect one or more erroneous indications that the signal from said
another transmitter was detected.
12. The apparatus of claim 10, wherein the sensing information
indicates whether the signal from said another transmitter has been
detected in one frequency band.
13. The apparatus of claim 10, wherein the sensing information
indicates whether the signal from said another transmitter has been
detected in any of a plurality of frequency bands.
14. The apparatus of claim 13, comprising: circuitry configured to
ascertain beamforming parameters on a per-frequency-band basis,
wherein for each frequency band, corresponding beamforming
parameters enable the main node to transmit within one or more
predefined geographical areas except for any portion of a
predefined area located on a far side of one or more exclusion
boundaries associated with the frequency band.
15. The apparatus of claim 10, comprising: circuitry configured to
modify beamforming parameters over time in correspondence with
modifications in transmission activity of said another
transmitter.
16. The apparatus of claim 10, comprising: circuitry configured to
receive, from each one of two or more remote sensors, sensing
information that indicates whether a signal transmitted by a
transmitter associated with the main node was received at or above
a predefined threshold power level in any portion of the predefined
area located on the far side of the one or more exclusion
boundaries.
17. The apparatus of claim 16, comprising: circuitry configured to
adjust the beamforming parameters if the sensing information does
indicate that the signal transmitted by the transmitter associated
with the main node was received at or above the predefined
threshold power level in any portion of the predefined area located
on the far side of the one or more exclusion boundaries.
18. The apparatus of claim 17, comprising: circuitry configured to
operate apparatus circuitry iteratively until the sensing
information does not indicate that the signal transmitted by the
transmitter associated with the main node was received at or above
the predefined threshold power level in any portion of the
predefined area located on the far side of the one or more
exclusion boundaries.
Description
BACKGROUND
[0001] The present invention relates to wireless communications,
and more particularly to the sensing and protecting of wireless
transmissions from a user of a spectral resource.
[0002] The radio spectrum is a limited resource that should be
shared between many different types of equipment such as cellular,
home network, broadcast, and military communication equipment.
Historically, each part of the radio spectrum has been allocated
(e.g., in a country- or region-wide basis) to a certain use (called
a "licensed" and/or "primary" use), such as only for television
("TV") or only for particular types of wireless communications.
This strategy has resulted in all applications/uses being
disallowed on the allocated carrier frequency except for those
applications included in the license agreement.
[0003] There are clear advantages to using dedicated spectrum for
wireless communications at least in that, because the frequency
band in question is reserved, no interference from other systems
should occur. This yields predictable network capacity and quality
of service.
[0004] However, in practice, the dedication of portions of the
radio spectrum to one or only a few types of users results in large
parts of the radio spectrum being unused much of the time. For
instance, in the Ultra-High Frequency (UHF) band, where TV
broadcasts take place, large geographical areas are unused, mainly
due to the large output power needed for such applications; this
large output power compels a large reuse distance in order to
minimize the risk of interference. An example of such geographical
areas within Scandinavia is illustrated in FIG. 1. In FIG. 1, the
shaded areas represent geographic locations in which a given
carrier frequency is being used by a licensed user (e.g., by
Broadcast TV). In the remaining areas, the so-called "white
spaces", the given carrier frequency is allocated to the licensed
user but is not actually being used by that user.
[0005] In order to make better use of the licensed spectral
resources, some countries will, in the future, allow unlicensed
services (so called "secondary" uses) to take place in areas
(called "white spaces") in which the licensed (primary or
"incumbent") user is not transmitting. However the
primary/incumbent user will always have priority for the use of the
spectrum to the exclusion of others. Therefore, some sort of
mechanism needs to be in place to ensure that there is only a low
probability that the unlicensed users are causing interference to
the licensed user.
[0006] One mechanism is to install the unlicensed network in a
geographical area where at least some parts of the licensed spectra
are known to be unused.
[0007] However, even more use of the white space can be made if the
non-interference mechanism adopts a detection strategy in which it
operates on the licensed frequency (or frequencies) in the white
space only so long as no licensed user transmissions are detected,
and ceases such operation as soon as licensed user transmissions
are detected. In this context, ceasing operation may mean ceasing
all operation, or alternatively may mean ceasing operation only on
those frequencies that are detected as being "in use", and
otherwise continuing to operate on other frequencies in the white
space. The most straightforward sensor is a signature detector
adapted to detect specific signatures transmitted from the
licensed/primary user (typically implemented as a matched filer).
An example of a white space system currently being standardized is
IEEE 802.22. An overview of this system can be found in Cordeiro et
al, "IEEE 802.22: An introduction to the First Wireless Standard
based on Cognitive Radios", Journal of Communications, Vol 1, No 1,
April 2006.
[0008] In commercial embodiments, the higher cost of signature
detectors may make them unfeasible. As a less expensive
alternative, sensors can be implemented to function as received
power detectors. These essentially compare a received power level
on a white space given frequency and compare this with a threshold
level. So long as the received power level is below the threshold
power level, the incumbent equipment can be considered to not be in
use.
[0009] Both of the previously described approaches of ascertaining
white space spectrum availability are, in a sense, all-or-nothing
approaches. When the lack of interference to the incumbent is
ensured by the choice of the geographical location, the white space
spectrum utilization is static in its nature. Thus, only the
location and frequency band combinations with no activity at any
time are considered, which may be a significant limitation. When
the sensor signals are used as spectrum availability indications,
the frequency band in question is activated or deactivated in the
whole area.
[0010] It remains a desirable goal to provide improved methods and
apparatuses that allow non-incumbent equipment to operate in a
white space area without disturbing operation by incumbent
equipment.
SUMMARY
[0011] It should be emphasized that the terms "comprises" and
"comprising", when used in this specification, are taken to specify
the presence of stated features, integers, steps or components; but
the use of these terms does not preclude the presence or addition
of one or more other features, integers, steps, components or
groups thereof.
[0012] In accordance with one aspect of the present invention, the
foregoing and other objects are achieved in methods and apparatuses
in which mobile communication system equipment is operated in a
manner that avoids interfering with another transmitter's use of a
spectral resource, wherein the mobile communication system
equipment includes a main node that serves a plurality of user
equipments. Such operation includes operating the main node to
receive, from each one of two or more remote sensors, sensing
information that indicates whether a signal from said another
transmitter has been detected, wherein each of the remote sensors
is situated at a respective one of two or more sensor locations.
The sensing information and information about the sensor locations
is used to ascertain one or more exclusion boundaries needed to
avoid interfering with the other transmitter's use of the spectral
resource. Beamforming parameters that will enable the main node to
transmit within one or more predefined geographical areas except
for any portion of a predefined area located on a far side of the
one or more exclusion boundaries are ascertained, and two or more
adjusted signals are produced as a function of the beamforming
parameters and one or more signals to be transmitted. The two or
more adjusted signals are then transmitted from respective ones of
two or more antennas.
[0013] In some embodiments, correlation results are generated by
correlating information about detected transmissions of the other
transmitter with information about contemporaneous transmissions of
the mobile communication system. The correlation results are used
to detect one or more erroneous indications that the signal from
said another transmitter was detected.
[0014] In an aspect of some embodiments consistent with the
invention, the sensing information indicates whether the signal
from the other transmitter has been detected in one frequency
band.
[0015] In some alternative embodiments, the sensing information
indicates whether the signal from the other transmitter has been
detected in any of a plurality of frequency bands. In some of such
embodiments, it is further possible to ascertain beamforming
parameters on a per-frequency-band basis, wherein for each
frequency band, corresponding beamforming parameters enable the
main node to transmit within one or more predefined geographical
areas except for any portion of a predefined area located on a far
side of one or more exclusion boundaries associated with the
frequency band.
[0016] In yet other alternative embodiments, beamforming parameters
are modified over time in correspondence with modifications in
transmission activity of said another transmitter.
[0017] In still other embodiments, operation includes receiving,
from each one of two or more remote sensors, sensing information
that indicates whether a signal transmitted by a transmitter
associated with the main node was received at or above a predefined
threshold power level in any portion of the predefined area located
on the far side of the one or more exclusion boundaries. The
beamforming parameters can be adjusted if the sensing information
does indicate that the signal transmitted by the transmitter
associated with the main node was received at or above the
predefined threshold power level in any portion of the predefined
area located on the far side of the one or more exclusion
boundaries.
[0018] In still another aspect of some embodiments, this sensing
and beamformer adjusting operation is performed iteratively until
the sensing information does not indicate that the signal
transmitted by the transmitter associated with the main node was
received at or above the predefined threshold power level in any
portion of the predefined area located on the far side of the one
or more exclusion boundaries.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The objects and advantages of the invention will be
understood by reading the following detailed description in
conjunction with the drawings in which:
[0020] FIG. 1 illustrates geographical areas constituting so-called
"white spaces" located in Scandinavia.
[0021] FIG. 2 is a block diagram of an exemplary system in which
various aspects of the invention are deployed and utilized.
[0022] FIG. 3 illustrates a cellular service coverage area
configured to avoid interference with an incumbent equipment's
service area, in accordance with an aspect of the invention.
[0023] FIG. 4 is, in one respect, a flow chart of
steps/processes/functions, carried out by an exemplary main node
consistent with the invention to enable the main node to modify its
coverage area in a way that avoids interfering with an incumbent
system's use, while still providing a meaningful level of service
to a remaining geographical area.
[0024] FIG. 5 is a block diagram of an exemplary main node adapted
with circuitry configured to carry out various aspects of the
invention.
DETAILED DESCRIPTION
[0025] The various features of the invention are described with
reference to the figures, in which like parts are identified with
the same reference characters.
[0026] The various aspects of the invention will now be described
in greater detail in connection with a number of exemplary
embodiments. To facilitate an understanding of the invention, many
aspects of the invention are described in terms of sequences of
actions to be performed by elements of a computer system or other
hardware capable of executing programmed instructions. It will be
recognized that in each of the embodiments, the various actions
could be performed by specialized circuits (e.g., analog and/or
discrete logic gates interconnected to perform a specialized
function, application specific integrated circuits made in
accordance with logic flows described herein, etc.), by one or more
processors programmed with a suitable set of instructions, or by a
combination of both. The term "circuitry configured to" perform one
or more described actions is used herein to refer to any such
embodiment (i.e., one or more specialized circuits and/or one or
more programmed processors). Moreover, the invention can
additionally be considered to be embodied entirely within any form
of computer readable carrier, such as solid-state memory, magnetic
disk, or optical disk containing an appropriate set of computer
instructions that would cause a processor to carry out the
techniques described herein. Thus, the various aspects of the
invention may be embodied in many different forms, and all such
forms are contemplated to be within the scope of the invention. For
each of the various aspects of the invention, any such form of
embodiments as described above may be referred to herein as "logic
configured to" perform a described action, or alternatively as
"logic that" performs a described action.
[0027] Modern base stations and mobile terminals typically include
two or more antennas to enable the use of Multiple Input Multiple
Output (MIMO) techniques during data reception and/or transmission.
In an aspect of embodiments consistent with the invention, white
space spectrum availability is increased by using signals from a
set of spatially distributed sensors to determine the regions of
potential inference to the incumbent spectrum owner. In another
aspect, the multiple transmitter antennas associated with wireless
network base stations are used to beam-form the transmitted signals
so that the areas of potential interference are excluded. The
beam-forming may be done on a per-frequency-band basis, in order to
maximize the usage of each frequency band.
[0028] These and other aspects will now be described in further
detail in the following.
[0029] In order to provide a context for understanding the utility
of embodiments consistent with the invention, an application will
be presented in which a cellular communication system having mobile
terminals (so-called "User Equipments", or "UEs") served by a
serving base station are called upon to perform white space sensing
due to their unlicensed operation in a white space, as discussed in
the Background section above. The base station adapts its operation
in accordance with the sensing results. It will be understood that
this context is presented merely for the purposes of illustration
and is not intended to limit the scope of the invention. To the
contrary, those of ordinary skill in the art will recognize that
many types of networks other than cellular telecommunication
systems may be adapted in accordance with the various inventive
principles to enable white space operation in a manner that avoids
interfering with incumbent equipment.
[0030] FIG. 2 is a block diagram of an exemplary system in which
UEs are configured to perform white space sensing, the results of
which are reported to a base station which then adapts its
operations accordingly. In this example, a licensed user (LU) 201
is depicted operating within a geographic area that includes a
white space 203. Transmissions of the licensed user 201 are
intended to be received by, for example, one or more licensed
receivers, only one of which (the licensed receiver 205) is
depicted. A mobile communication system is configured in accordance
with various aspects of the invention to permit it to operate as an
unlicensed user within the white space 203. The mobile
communication system includes a serving base station 207 that
serves one or more UEs, including the UEs 209, 211, 213, and 215.
In the context of the invention, the base station 205 exemplifies a
"main node" that comprises circuitry configured to perform the
functions described below. In other embodiments different equipment
constitutes the "main node." For example, in WLAN systems, a router
can operate as a main node in the context of the invention. To
facilitate readability of this document, the well-known term "base
station" is used herein as a generic term that covers not only base
stations in the traditional sense, but also all forms of radio
access nodes in all forms of radio access technologies, of which
cellular communication equipment and WLAN technology are but two
examples.
[0031] Each of the UEs 209, 211, 213, and 215 includes circuitry
configured to perform white space sensing in any of a number of
ways. For example, as mentioned in the Background section, the most
straightforward sensor is a signature detector adapted to detect
specific signatures transmitted from the licensed/primary user
(typically implemented as a matched filer). Alternatively, the
circuitry configured to perform white space sensing can be
implemented as a power level detector, also as described in the
Background section. The sensing data generated by the UEs 209, 211,
213, and 215 is communicated to the base station 207 which, as will
be described further in connection with FIGS. 3, 4, and 5, includes
circuitry configured in accordance with the inventive principles
described herein to enable some level of unlicensed operation while
avoiding interference to the licensed user 201.
[0032] A typical white space network WS NW has a network of sensors
distributed over the planned coverage area. These can be either
wireless units as just discussed (e.g., special-purpose units,
modified UEs, or standard user terminals) or wired units. The
location of all the sensors is roughly or exactly known. By
associating the information contained in the reporting signals with
the locations of the reporting sensors, the network can construct
an interference map (i.e., identify the areas where the incumbent
signals are and are not present).
[0033] Modern base stations typically are equipped with 2-4
transmitter (TX) antennas per sector. In accordance with an aspect
of embodiments consistent with the invention, the several
transmitter antennas are used in an interference avoidance strategy
as follows.
[0034] It is well known that multiple antennas may be used for
precoding and beamforming. Beamforming is achieved by transmitting
the same signal from all antennas, but applying individual phase
shifts and attenuation values to the individual antenna signals. By
suitably choosing these values, as well as by using electrical
downtilt features, the beam shapes may be tuned quite exactly,
resulting in exact desired coverage patterns.
[0035] In traditional networks, beamforming is used to direct
signal energy towards the intended recipient(s) of the signal.
However, in embodiments consistent with an aspect of the invention,
rather than directing a beam towards a particular target, a
completely different approach is taken in which beam shapes are
tuned in a manner that excludes particular geographical regions,
and in the context of white space operation, excludes those
geographical regions in which incumbent signals have been detected
within the network's standard coverage area. This coverage
modification concept is illustrated graphically in FIG. 3.
[0036] In particular, a base station 301 serves UEs located in any
of three cell sectors: a first sector 303, a second sector 305, and
a third sector 307. Three incumbent communication systems are
located in the vicinity, represented in this example by three
television transmitters: a first television transmitter ("TV1"), a
second television transmitter ("TV2") and a third television
transmitter ("TV3"). The first, second and third television
transmitters TV1, TV2, TV3 have respective first, second, and third
signal coverage areas 309, 311, 313. Each signal coverage area is a
geographical region within which a signal transmitted by the
associated television transmitter is strong enough to, with a given
probability, be "heard" and therefore received by a receiver.
[0037] In the present example, the first and second signal coverage
areas 309, 311 overlap portions of the cell sectors 303, 305, 307,
whereas the third coverage area 313 does not. In accordance with an
aspect of embodiments consistent with the invention, the base
station 301 determines those portions of its first, second and
third sectors 303, 305, 307 that should be excluded from its
service areas. In this example, these are first and second
exclusion areas 315, 317, which are defined by respective first and
second exclusion boundaries 319, 321. Each of the exclusion
boundaries 319, 321 has a "near side" and a "far side", wherein the
"near side" is that side of the exclusion boundary 319, 321 closest
to the base station 301, and the "far side" is that side of the
exclusion boundary 319, 321 farthest from the base station 301.
That is, because of reports from sensors (not shown in FIG. 3)
located within the first, second and third sectors 303, 305, 307,
and knowledge about the locations of those sensors, the base
station 301 is able to determine the first and second exclusion
boundaries 319, 321. It then uses beamforming-related techniques to
exclude geographical areas from its service coverage areas, wherein
the excluded geographical areas are defined as being those
geographical areas that lie on the far side of the exclusion
boundary.
[0038] FIG. 4 is, in one respect, a flow chart of
steps/processes/functions, carried out by an exemplary main node
(e.g., a base station in a cellular communications system)
consistent with the invention to enable the main node to modify its
coverage area in a way that avoids interfering with an incumbent
system's use, while still providing a meaningful level of service
to a remaining geographical area. In another respect, FIG. 4 can be
considered to depict the various elements of circuitry 400
configured to carry out the various functions described in FIG. 4
and its supporting text.
[0039] The main node receives sensor signals from the various
sensors located within the predefined geographical area (e.g.,
cell) served by the main node (step 401). The information conveyed
by each of the sensor signals provides some sort of indication at
least about whether the sensor that generated the sensor signal
detected a signal from an incumbent user.
[0040] The main node then uses the information conveyed by the
sensor signals in conjunction with information about the location
of the sensors that generated the sensor signals to determine what,
if any, exclusion boundaries are needed to avoid interfering with
incumbent equipment's signals (step 403). Of course, if no
incumbent equipment's signals are detected, then there will not be
any exclusion boundaries and the main node is free to utilize the
entire predefined geographical area that it serves.
[0041] But, assuming that signals from one or more incumbent
equipments have been detected, the shape and location(s) of the
exclusion boundaries can be determined in any of a number of ways
including, but not limited to, the following alternative
embodiments:
[0042] If the sensors deliver a single-bit signal (e.g., indicating
incumbent detected/not detected) and the density of detectors is
low, then the exact shape of the exclusion boundary (or boundaries)
may be difficult to determine. In such cases, the exclusion
boundary may be approximated as the convex hull of the sensors
returning positive signals, plus a guard area. For example, if all
of the sensors supplying a positive signal (i.e., signal detected)
were to be replaced by vertical poles extending up from the ground,
then the convex hull would be defined by the shortest rope that
could be spanned around all of the poles. As a further note, if the
pattern of poles has concavities (i.e., if concavities would be
formed if a line were drawn from each pole to its neighbors) then
the rope would not touch all of the poles on its shortest way
around them.
[0043] If the sensor density is large, the true edges of each
exclusion boundary may be determined by observing the boundary
where closely-spaced sensors return differing messages. That is,
the exclusion boundary will lie somewhere between a sensor
reporting detection of an incumbent equipment and a sensor
reporting non-detection of an incumbent equipment.
[0044] In yet another alternative, if the sensors are configured to
also report the detected incumbent signal strength or signal
quality measures, then the exclusion boundary can be determined by
interpolating or extrapolating the signal strength decay
curves.
[0045] These are but examples of ways in which the exclusion
boundary (or boundaries) can be determined. In practice, those of
ordinary skill in the art will readily be able to configure other
embodiments if other information (e.g., more precise) information
is provided from the sensor regarding characteristics (e.g., signal
quality, direction) of the detected incumbent signal.
[0046] Assuming that one or more exclusion boundaries are
determined, the circuitry in the main node then ascertains
beamforming parameters to transmit signals from the main nodes
antennas throughout the predefined geographical area (e.g., cell)
except for any portion of the predefined geographical area located
on the far side of an exclusion boundary (step 405). The details of
how to derive these parameters need not be described here because
this particular problem reduces to an antenna array or
multi-antenna system design problem, the solution to which is well
within the capability of one or ordinary skill in the art. However,
whereas conventional multi-antenna system design problems relate to
directing a beam towards a target area (and therefore focusing the
mathematics on the maxima of the resulting antenna directivity
patterns), aspects of embodiments consistent with the invention
focus on directing transmissions away from a certain area or areas.
This means that those of ordinary skill in the art can use known
equations, but in this case pay attention to those areas of
resulting antenna directivity patterns associated with nulls or
close to nulls. It will be appreciated that this may lead to
different approximations being used (associated with minima) in
embodiments of the invention than are conventionally used when
beamforming towards a target area (maximum) is considered.
[0047] Two or more adjusted signals are then produced at least as a
function of the beamforming parameters and one or more signals to
be transmitted (step 407). For example, the beamforming can be
applied to at least a portion of the transmitted power, the portion
being great enough to, in combination with the resulting
transmission antenna pattern, result in only a low, allowed, signal
strength being receivable in the exclusion area(s). Each of the
adjusted signals is then transmitted from a respective one of two
or more antennas associated with the main node (step 409), the
result being that the main node's transmitted signals will avoid
entering any of the exclusion areas.
[0048] FIG. 5 is a block diagram of an exemplary main node (e.g.,
base station) 500 adapted with circuitry configured to carry out
various aspects of the invention. For the sake of clarity, only
those components having particular relevance to the invention are
depicted. Those of ordinary skill in the art will readily
understand that the main node 500 also includes other circuitry
(not depicted) that is well-known in the art and therefore need not
be described herein.
[0049] The main node 500 operates as a transceiver, and therefore
includes receiver circuitry 501 as well as transmitter circuitry
503. For example, when the main node 500 is a base station serving
one or more UEs in a mobile communication system, the receiver
circuitry 501 receives signals from the UEs in an uplink direction,
and the transmitter circuitry generates signals intended for
receipt by the UEs in a downlink direction. In this exemplary
embodiment, the main node 500 comprises a plurality, N, of antennas
505-1, . . . , 505-N, which are shared between reception and
transmission operations. In alternative embodiments, the receiver
and transmitter sections of the main node 500 have their own
dedicated antennas, with at least the transmitter sections having a
plurality of antennas.
[0050] The main node 500 further comprises white space control
circuitry 507 that generates control signals that cause various
circuit elements within the main node 500 to carry out the
functions described herein, such as but not limited to the
functions depicted in FIG. 4 and described in that figure's
corresponding text. The white space control circuitry can be a
separate element within the main node 500, or can alternatively be
partially or fully integrated with other controller elements within
the main node 500.
[0051] As mentioned above, the receiver circuitry 501 receives
signals from one or more UEs. When the signals are associated with
"normal" data communication functions, they are passed along as
"received information" for further processing, the particularities
of which is beyond the scope of the invention. However, the
receiver circuitry 501 also receives sensor signals from the
sensors located within the main node's service area (e.g., cell),
and extracts the sensor information from these signals. The sensor
information is supplied to the white space control circuitry 507
which is configured to determine whether an incumbent equipment has
been detected, and if so, what exclusion boundaries are needed to
avoid interfering with the incumbent equipment's signals. The white
space control circuitry 507 will need to know not only what the
sensors are reporting (e.g., "detected"/"not detected"), but also
the locations of those sensors. This sensor location information
can be included expressly in the sensor information, or
alternatively the white space control circuitry 507 can derive
sensor location information from other information provided, for
example, as part of the sensor information.
[0052] The white space controller circuitry 507 then ascertains the
beamforming parameters that would enable transmission from of one
or more signals from the N antennas 505-1, . . . , 505-N in a
manner that serves the entire predefined geographical service area
except for any portion of that area that is located on a far side
of an exclusion boundary.
[0053] To further enable this function in this particular exemplary
embodiment (but not necessarily in alternative embodiments), the
main node 500 includes signal beamforming adjustment circuitry that
receives the signal(s) that would normally be generated by the
transmitter circuitry 503, and based on beamformer parameters
generated and supplied by the white space control circuitry 507,
produces two or more adjusted signals as a function of the
beamforming parameters and the one or more signals to be
transmitted. These signals are then supplied to respective ones of
the N antennas 505-1, . . . , 505-N so that the downlink signal(s)
will be transmitted by the main node 500 in a manner that will not
enter any of the identified exclusion areas.
[0054] The white space controller circuitry 507 can further be
adapted in alternative embodiments to perform other functions, such
as any one or combination of functions described below. Configuring
white space controller circuitry 507 to carry out any of these
functions, either through hardwired or programmable means, is well
within the capability of one of ordinary skill in the art.
[0055] Some alternative embodiments do not include the feature
wherein complex beamforming is applied to achieve filling the
entire available constrained coverage area as illustrated in, for
example, FIG. 3. In particular, if the white space is being used as
an additional carrier in a multi-carrier system (e.g., to provide a
boost in throughput), the beam forming is tailored for a single
scheduled user at a time. The incumbent activity area information
is then used to determine whether the use of white space spectrum
for the given user is permitted, or which parts of it are
available. That is, in this scenario only one UE at a time is using
the white space carrier; all other UEs in the cell are using
non-white space carriers, so no special precautions need to be
taken to avoid the service to these other UEs causing interference
to an incumbent user. As to the one UE that is using the white
space carrier, beamforming is applied not only to avoid
transmitting the white space carrier into any portion of the
predefined area (e.g., cell) located on a far side of an
exclusionary boundary, but also to enhance directivity towards that
one user.
[0056] In other alternative embodiments, interpreting the reports
from the sensors is correlated with information about the white
space network's (e.g., the main node's) own transmissions. The
presence of a correlation can then be interpreted as a "false
alarm", in which the white space network's own transmissions were
mistaken for an incumbent equipment transmission.
[0057] Another use of this correlation is to verify the beam
forming pattern. More particularly, the correlation values can be
used to estimate reception conditions of the white space network's
own transmissions at different parts of the cell area. These
detected reception conditions are compared with what was intended
to be achieved by the current beamforming pattern. If it is found
that reception of these signals was too strong on the far side of
an exclusion boundary, this is an indicator that the model for
beamforming is not good enough. The system then responds by, for
example, moving that particular exclusion boundary closer to the
transmitter, recalculating new beamforming parameters, applying the
new parameters, and in some but not necessarily all embodiments,
doing this iteratively to arrive at beamforming parameters that are
considered to be sufficiently good (i.e., beamforming parameters
that achieve transmission results that meet one or more predefined
criteria).
[0058] In yet another aspect of some embodiments, the white space
operator can intentionally use its own signals, preferably before
an incumbent equipment is active, to perform beamforming
experiments that will better inform how best to generate
beamforming parameters. For example, different exclusion boundaries
can be hypothesized and the corresponding beamforming parameters
computed for these hypothesized exclusion boundaries. The white
space operator then employs these during one or more signal
transmissions. Sensor reports are then analyzed to determine
whether the beamforming parameters achieved the intended results
(i.e., of inhibiting transmission on a far side of a hypothesized
exclusion boundary). By honing the beamforming algorithms and/or
parameters in this way, the guard areas may be made smaller than in
other embodiments.
[0059] In practice, it may be the case that more than one white
space operator is operating in a given white space. In such cases,
the various aspects described above can be used not only to carve
out sections of a predetermined area that are known to be used by
incumbent equipment, but also to identify and then do the same for
another white space operator that is detected in the area.
[0060] For the sake of simplicity, the above description focused on
avoiding interference on a frequency band associated with incumbent
equipment. However, in yet another aspect that can be combined with
any other embodiments, the idea of using beamforming to avoid
exclusion areas associated with incumbent equipment can readily be
extended to encompass several frequency bands. In some of such
embodiments, the sensors return incumbent activity flags separately
for respective ones of several frequency bands (e.g., TV station
frequencies that may be active or inactive independent of each
other). For each band, the main node (e.g., base station) then
determines an appropriate beam pattern and applies it on a per-band
basis.
[0061] In still another aspect that can be combined with other
aspects, the beam patterns are modified as the incumbent activity
varies. In this way, not only is the spatial variability used, but
also the temporal variability of the incumbent activity is utilized
to maximize the white space network capacity.
[0062] The various aspects illustrated by the above exemplary
embodiments provide significant advantages over prior systems. For
example, a typical white space wireless communications network
deployment motivation is expected to be extending the available
spectrum for an already deployed network, operating in dedicated
spectrum. As such, the availability of the extra spectrum in all
areas at all times is not critical, but maximizing spatial and
temporal coverage is if course highly desirable. Embodiments
consistent with the invention provide a tool for doing just that.
As a result, utilization of both network capacity and capital
expenditure is increased, and the subscribers' user experience is
improved.
[0063] Also, for greenfield operators that can launch a white space
network with some part of spectrum guaranteed by design (e.g., the
choice of geographical area), the inventive aspects exemplified by
the above-described embodiments provide a way to utilize possible
additional white space spectrum that may be sporadically available
in the coverage area.
[0064] The invention has been described with reference to
particular embodiments. However, it will be readily apparent to
those skilled in the art that it is possible to embody the
invention in specific forms other than those of the embodiment
described above. Thus, the described embodiments are merely
illustrative and should not be considered restrictive in any way.
The scope of the invention is given by the appended claims, rather
than the preceding description, and all variations and equivalents
which fall within the range of the claims are intended to be
embraced therein.
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